Conventionally, it has been known that there is a correlation between pulse wave velocity or time, calculated from the pulse waveform or the electrocardiographic waveform measured at two points, and blood pressures. Therefore, there have been developed methods in which a sensor device attached to the body of a subject measures the pulse wave velocity and estimates the blood pressure continuously with the purpose of maintaining the physical condition and health, or catamnestic observation. Currently, biosignal-measuring devices for measuring the pulse wave and the electrocardiogram signals are being miniaturized and made to communicate wirelessly. In the future, it is expected biosignal-measuring devices may be worn continuously by a subject in daily life, and the biosignal-measuring device will estimate blood pressure, or the like, continuously over a long period by determining such things as the pulse wave velocity from the pulse wave signal and/or an electrocardiogram.
But it is expected that when a signal device is continuously worn in daily life the signal measuring device may move or be moved on occasion and such movement may prevent or interrupt the continuous measurement process, and thus render the signal measuring device inoperative or otherwise lessen the utility of such a signal measuring device.
In the continuous measurement or calculation of a biosignal such as blood pressure, if the obtained value varies significantly or the obtained value deviates from a specified range, it may be possible to determine that an abnormal event occurred. However, if the measurement is suspended temporarily, sometimes it is not possible to determine whether the significant variation of the measured or calculated value, or deviation from the specified range is caused by the variation of the targeted biosignal or by the change in a condition such as the measuring position.